Remote flow transducer for communication cable

ABSTRACT

A method and apparatus for remotely monitoring air leakage in communication cables is disclosed. Improved volume flow meters are remotely attached at the air inlet to manhole mounted manifolds for supply of dehumidified air to telephone cables. Dehumidified air passes through the remote meters into the manifolds and then interior of a sheath of a communication cable wherein the discrete conduits can be kept dry and under air pressure. The remote volume flow meter at each manifold includes a diaphragm having an air flow conduit mounted in movable opposition to a variable area orifice. The diaphragm actuates a variable resistor, which preferably includes a tailored neutral density wedge. This tailored neutral density wedge moves with the diaphragm towards and away from a position between a light source (typically a light-emitting diode) and a photo sensor (typically of the photo resistor variety). The volume flow meter receives its power through and also has its output communicated through a single pair of wires. Powering of the light source occurs through an alternating current path consisting of a transformer secondary and regulator. Monitoring of the photo sensor output occurs by coupling the photo sensor element in series with the transformer primary and bypassing the alternating current path with a capacitor shunt. As a result, a remotely located meter, when dialed or remotely sampled, can indicate by variable penetration of the neutral density wedge, a changing resistance which is directly related to diaphragm position, and hence flow through the meter. This signal from a remote manhole location can be monitored from a distant central monitoring station, such as a central telephone office. Through a network of such flow meters in combination with conventional pressure transducers, cable air leaks can be detected, rapidly measured as to their suspected severity, and located with improved precision for timely repair.

This is a continuation of application Ser. No. 520,192, filed Nov. 1,1974, now U.S. Pat. No. 4,007,628.

This invention relates to air flow meters and particularly to a remotelylocated air flow meter which is capable of being periodically monitoredto indicate air flow.

STATEMENT OF PROBLEM

Communication conduits are individually bound together in sheathedcables. It is common for air to be communicated interior of the sheathof such cables. This air has about two percent humidity and isintroduced into the cable sheath at about ten pounds pressure. This airserves to maintain the individual conduits in a dry condition.Additionally, if leaks occur in the cable sheath, the outward passage ofair prevents the inward penetration of water interior of the cable.Moreover, where the leak in the sheath can be located, the potentialpoint of entry of moisture can be patched and the dry and dehumidifiedair ambient interior of the individual communication conduits within thecable preserved.

It should be noted that cables are provided with numerous patchedplaces, especially where individual conduits are threaded through thecable sheath to and from a major cable or trunk line. Moreover, cablesare cross-conducted by "stubbing". At these locations, air can flow outof the cable sheath and can cross-flow between cables.

SUMMARY OF THE PRIOR ART

Heretofore, pressure only has been remotely measured in such cablesystems. Typically, pressure has been measured in half pound incrementsremotely on a zero to ten pounds per square inch scale.

An example of a typical prior art system includes a single manifoldhaving five outlets, each pressurizing an individual cable sheathenclosing 1200 and 2600 pairs of wires. Heretofore, each of these cableshas been remotely measured with pressure transducers. Typically, thepressure transducers are placed at 5,000 foot intervals preferablylocated exactly between manifolds.

When an air leak occurs, typically more air is bled into the system.Often, this results in substantially the same pressure being maintainedin the line in the area of the remote pressure transducer. This pressureis maintained until the line leakage exceeds the capacity of the systemto supply dehumidified air at which point the pressure drops, moisturepenetrates and communication is lost.

Moreover, the precise location of sheath leaks in cable systems has beenextremely difficult to detect. Where a leak occurs at or near a manifoldand remote from an intermediate pressure transducer, a high volume flowof air results with a low pressure drop at the pressure transducer.Moreover, when a puncture of a cable sheath occurs, a period of timeelapses during which the cable sheath deflates. This deflation takestime. The result is that the location of leaks is slow. Moreover, thedemoisturizing pressure of dehumidified air is lost before the severityof the cable sheath puncture is discovered. Before the severity of asheath puncture can be evaluated and overtime judgments properly made bymaintenance personnel, interruption of communication results.

Attempts have been made to meter air flow. Heretofore, the meteringshave occurred adjacent the pump at a central dehumidifying station.Metering at this location can only grossly evaluate an entire cableregion and is of little or no help in locating or evaluating withprecision cable sheath punctures.

Metering at the individual manholes in which air flow manifold andconduit are located has also occurred. Typically, technicians are sentto individual manhole, required to open them, read the meters, and thenproceed to adjacent manholes. Considerable time is used. Readings fromone manhole to another are often confused. The end result is thatindividual sheath leaks cannot be satisfactorily located within asufficient time interval to permit economic repair.

SUMMARY OF THE INVENTION

A method and apparatus for remotely monitoring air leakage incommunication cables is disclosed. Improved volume flow meters areremotely attached at the air inlet to manhold mounted manifolds forsupply of dehumidified air to telephone cables. Dehumidified air passesthrough the remote meters into the manifolds and then interior of asheath of a communication cable wherein the discrete conduits can bekept dry and under air pressure. The remote volume flow meter at eachmanifold includes a diaphragm having an air flow conduit mounted inmovable opposition to a variable area orifice. The diaphragm actuates avariable resistor which preferably includes a tailored neutral densitywedge. This tailored neutral density wedge moves with the diaphragmtowards and away from a position between a light source (typically alight-emitting diode) and a photo sensor (typically of the photoresistor variety). The volume flow meter receives its power through andalso has its output communicated through a single pair of wires.Powering of the light source occurs through an alternating current pathconsisting of a transformer secondary and regulator. Monitoring of thephoto sensor output occurs by coupling the photo sensor element inseries with the transformer primary and bypassing the alternatingcurrent path with a capacitor shunt. As a result, a remotely locatedmeter, when dialed or remotely sampled, can indicate by variablepenetration of the neutral density wedge, a changing resistance which isdirectly related to diaphragm position, and hence flow through themeter. This signal from a remote manhole location can be monitored froma distant central monitoring station, such as a central telephoneoffice. Through a network of such flow meters in combination withconventional pressure transducers, cable air leaks can be detected,rapidly measured as to their suspected severity, and located withimproved precision for timely repair.

OBJECTS AND FEATURES OF THE INVENTION

An object of this invention is to place a meter sampled by remotedialing equipment, which meter can indicate flow at a manhole locationdistant from a central monitoring station, such as a central telephoneoffice.

An advantage of this aspect of the invention is that changes of flowprovide a more immediate indication of sheath puncture. The proximity ofthe leak can be detected with improved accuracy. Moreover, deflation ofthe cable sheath need not occur completely before corrective action isundertaken.

An additional advantage is that by a programmed sampling of a number ofremote air flow devices, a relative change in flow can be detected. Theseverity of a leak in the cable sheath can be evaluated. Overtimejudgment by maintenance supervisory personnel can be made withprecision.

Yet another advantage of this invention is that the on site measurementof flow at remote manholes is no longer required.

Yet a further advantage of this invention is that "routining" orsystematic reduction of sheath cable leaks in a given cable area can beremotely monitored. The performance of crews operating remotely fromtheir supervisor can be more accurately judged.

Yet another advantage of this aspect of the invention is that the flowmeter device can be used in conjunction with existent pressuremonitoring equipment by combining the output of flow measurement withexistent pressure measurement. Leak detection, location and evaluationis vastly improved.

Yet another advantage of this invention is that the number of monitoreddevices (whether they be pressure detectors or flow detectors inaccordance with this invention) can be vastly reduced. Thus, cableconduits which were heretofore used for monitoring the cable sheath airsystem can be freed for revenue producing results.

A further object of this invention is to disclose a flow meter whichprovides for flow measurement with low pressure drop of dehumidified gaspassing through to the meter. According to this aspect of the invention,each measurement device includes a diaphragm having an air flow conduitmounted in movable opposition to a variable area orifice. Low flowproduces low orifice area. High flow produces high orifice area.

An advantage of this aspect of the invention is that the entire flow toa cable sheath manifold can be passed through the device.

Another advantage of the configuration of the variable orifice anddiaphragm is that they are insensitive to vertical positioning of theflow meter. The flow meter can be placed at any alignment which isconvenient to its installation; it is not required that it be placed inone position with respect to gravity.

Yet another advantage of the variable orifice and diaphragm is that themeter itself is capable of being designed to function as a check valve.Should pressure at the pump be lost, an air flow will occur from thecable toward the air pump. Air flow can be arrested at the meter.

A further object of this invention is to disclose a single two-wirecircuit that simultaneously powers and monitors remote flow. Powering ofthe light source, typically a lightemitting diode, occurs through analternating current path consisting of a transformer secondary andregulator. Metering of the photoconductive output occurs by coupling thephotosensitive element in series with the transformer primary andbypassing the alternating current path with a capacitor shunt.

An advantage of this aspect of the invention is that each flow meteronly uses a single pair of wires. Minimum use of lines results. Theremaining communication conduits can be turned over to revenuegenerating communication.

An additional advantage of the monitoring circuit which results is thatit can be used with remote sampling pressure sensing equipment. As itnow exists, minimum modification to remote sampling equipment isnecessary.

Yet another object of this invention is to disclose in combination withthe diaphragm and variable flow orifice an electronic signal which, withsubstantial linearity, indicates detected flow. According to this aspectof the invention, a tailored neutral density wedge penetrates withdiaphragm movement into the interstitial area between a light source andphoto detector. The wedge, light source and detector are all containedinternally of the meter.

An advantage of this aspect of the invention is that the wedge, lightsource and photo sensor are all contained in a dark, dry environmentwhere maximum life with minimum interference from the operating ambientoccurs.

An additional advantage of the neutral density wedge is that it can betailored for virtually any non-linearity encountered in the system. Forexample, differing components of differing elasticity in the diaphragmor opposing spring can be accommodated by empirically determined wedgedensity changes.

Yet another advantage of this invention is that the device is completelyenclosed. As such, it is substantially tamperproof. Maintenancepersonnel cannot alter the device to correspondingly alter evaluation oftheir performance.

Yet another advantage of this device is that tampering with air sheathsystems in cables can be more immediately detected with the moreimmediately detectable change of flow.

Other objects, features and advantages of this invention will becomemore apparent after referring to the following specification andattached drawings in which:

FIG. 1 is a schematic view of three flow meters, three pressure sensors,and a single cable, all monitored from a central location which suppliesdehumidified air;

FIG. 2 is a perspective view shown broken away illustrating the interiorcomponents of the improved remote sampled flow meter;

FIG. 3 is a section taken through the flow meter of FIG. 2 illustratingthe relative positions of the light source, neutral density wedge andphoto sensor;

FIG. 4 is an enlarged perspective of the variable area orifice shownbroken away to illustrate the change of orifice area with meterdiaphragm movement;

FIG. 5 is a schematic of the circuitry used for monitoring flow meteroutput, showing in the left-hand portion the telephone office circuitry,showing in the right-hand portion the circuitry in the meter, andillustrating schematically only conventional switching circuitry therebetween; and,

FIG. 6 is a graph illustrating one embodiment of density versusdisplacement which is satisfactory for the construction of the neutraldensity wedge useful with this invention.

Referring to FIG. 1, central telephone exchange A is illustrated havingmonitoring equipment B and pump C supplying dehumidified air of twopercent humidity under pressure to main outflow conduit D. Conduit D inturn flows to manifold conduit E through the improved remotely sampledflow meter F of this invention, and then to manifold G. It will beunderstood that conduit E, flow meter F, and manifold G are typicallylocated within a manhole remote from the central exchange A.

It should be understood that monitoring equipment B is a knownsurveilance switching system. Specifically, the Cable PressureSurveilance System manufactured by the Pacific Telephone Company of SanFrancisco, Calif. can be used with modification of those having ordinaryskill in the art.

Dehumidified air supply to cable H is illustrated for only one cable.Typically, one of the outlets J from manifold G penetrates a cablesheath 14 containing typically 1200 to 2600 pairs of communicationconduits 16. Dehumidified air under pressure is provided. For example,air would be communicated to cable H at 5,000 foot intervals.

It should be noted that the insulation in many underground cables isextremely moisture sensitive. For example, many cables are insulated bypulp or paper insulation of very small wall thickness.

It is preferable to monitor cable sheath pressure interior of sheath 14for each cable H intermediate of the manifold connections at conduit J.To this end, conventional pressure transducers K are typically locatedintermediate the manifold G. Thus, the distance between the pressuremonitoring transducers K will be approximately 5,000 feet.

Moreover, it is desirable to monitor, with a conventional pressuretransducer L, the cable run at its remote end from the manifold.According to this aspect, a pressure monitor L is shown in the schematicof FIG. 1 at the end of a cable run.

Having set forth this much of the invention, the construction, andthereafter the operation of the flow measuring device, will be set forthwith respect to FIGS. 2, 3, 4 and 6. Thereafter, an explanation of thecircuitry monitoring the remotely located meters will be set forth withrespect to FIG. 5.

Referring to FIG. 2, flow meter F includes a lower cylindrical portion20 and an upper cylindrical portion 22, with a separating plate 23captured there between. Lower cylindrical portion 20 is provided with anair inlet 24. Similarly, upper cylindrical portion 22 is provided withan air outlet 25. As can be seen, the lower section of cylindricalportion 20 and the upper section of cylindrical portion 22 are bothclosed with respective circular end walls 28, 30.

The respective cylindrical portions 20, 22 are confronted at annularflanges 30, 32. These flanges capture there between plate 23 and gasketmaterial 33.

Gasket material 33 is shaped to a flexible bell shaped diaphragm formand extends upwardly of plate 23 into the interior volume defined by thecylindrical portion 22. It is the up and down movement of gasket 33which simultaneously determines the variable area of the orificeassembly 40 (see FIG. 4) and the penetration of the neutral densitywedge apparatus 50 (see FIG. 3).

The orifice assembly 40 is mounted on an interior pedestal 41. Theclosed end of cylinder portion 42 stands on pedestal 41. The open end ofcylinder portion 42 extends upwardly to and preferably through plate 23so as to communicate with air between plate 23 and the underside of thediaphragm material 33.

The closed cylindrical portion 42 of the orifice assembly 40 hasconcentrically mounted therein a tapered and preferably conical shaft 44with a centering cross 45. As will hereinafter become more apparent,tapered shaft 44 provides a changing orifice area with elastic movementof the diaphragm 33.

Diaphragm 33 is apertured at an aperture 46 which is typicallyconcentric. Aperture 46 is concentric of two diaphragm capturing disks47, 48.

A cylinder 49, at both ends, communicates at its lower end to closedcylinder 42 and communicates at its upper end through aperture 46 ingasket 33. Preferably, gasket 33 is biased downwardly by a compressioncoil spring attached to the gasket capturing disks 47, 48 at the lowerend of the coil spring, and to a concentric pall 52 at the upper end ofthe coil spring.

Ignoring for the present the function of the neutral density wedgeapparatus 50, the air flow interior of the meter can be explained.

Dehumidified air typically enters through orifice 24 interiorly to thelower cylindrical portion 20 of the flow meter. Air communicatesupwardly to the cylindrical interior and passes through plate 23 atapertures 53 (it being noted that one aperture 54 also provides for thepenetration of the neutral density wedge).

Referring to FIG. 4, air then enters into the top of the closed cylinder42 and passes downwardly into the interior of the cylinder. It reversesflow at the lower portion of open cylinder 49 and passes upwardly andout of cylinder 49 at concentric aperture 46.

Having described this flow pattern, the function of cylinder 49 incooperation with the gasket 33 and its opposed coil spring 51 can now bedescribed. It will be noted that cylinder 49 has an outside diameterless than the inside diameter of the closed cylinder 42. This is becausethe interstitial area between the two cylinders is required for downwardgas flow.

Moreover, it will be noted that centering cross 45 has an externaldiameter which is slightly less than the internal diameter of cylinder49. Thus, when cylinder 49 moves upwardly or downwardly, it will do soin centered relation to the closed cylinder 42.

It can just as plainly be seen that the preferably conical shape oftapered shaft 44 will define a smaller or a greater area at the lowerend of cylinder 49. If, for example, full penetration of cylinder 49interior of the closed cylinder 42 occurs, a minimum orifice area oreven orifice closure will result. Conversely, if cylinder 49 is almostcompletely withdrawn from closed cylinder 42, a large area orificeobstructed only by the centering cross 45 will result.

It should be noted at this juncture that the flow meter is capable ofbeing designed to function as a check valve. Assuming air pressure islost from pump C, full downward motion of cylinder 49 will result inclosure of the bottom aperture of the variable area orifice. Preventionof air flow from interior of cable sheath 14 toward pump C will result.

Diaphragm 33 and spring 51 provide for the variable penetration of thecylinder 49. Where a relatively high volume flow occurs through themeter, diaphragm 33 expands upwardly. This upward expansion drawscylinder 49 correspondingly upward. A large flow area to accommodatelarge meter flow results.

Conversely, where air flow is reduced, downward flexure of diaphragm 33urged by spring 51 results. Penetration of cylinder 49 interior of theclosed cylinder 42 results in a small flow area with correspondent smallflow through the meter.

Thus, the diaphragm and the variable area of the orifice cooperate witheach other. High flow generates expanding pressure on the diaphragm withcorrespondent high aperture flow area. Low flow reduces and collapsesthe diaphragm with correspondent low flow meter area.

Having set forth the function of the variable orifice flow meterapparatus 40, the operation of the neutral density wedge apparatus 50can be described.

Specifically, diaphragm 33 includes at its central portion a smallbracket 55 having a neutral density wedge 57 attached thereto.Typically, the neutral density wedge 57 extends vertically downward frombracket 59 through the aperture 54 in plate 23. This neutral densitywedge extends into an interval between a light source 60 (which istypically a light-emitting diode) and a photo sensor 62 (which istypically a photo resistive element).

Referring to the graph of FIG. 6, the construction of the neutraldensity wedge can be illustrated. The wedge typically is provided withan active penetration over the flexure of the diaphragm 33 ofapproximately 1.2 inches. The wedge itself is typically constructed ofphotographic film having a variable light transmissive property. Thisfilm of strip 57 becomes increasingly opaque with increasing penetrationof strip 57 downwardly between light source 60 and photo sensor 62. FIG.6 is an empirical plot of the increasing filtration of light uponincreasing penetration of the neutral density wedge 57 between the lightsource 60 and the photo sensor 62.

It has been previously emphasized that the neutral density wedge 57 is aconvenient mechanism to linearize all the irregularities which may becontained within the flow meter configuration. By the expedient ofmeasuring with other metering apparatus the flow through a typicalsample of flow meters of this invention, and thereafter tailoring thedensity of the neutral density wedge along an empirically determinedcurve such as shown in FIG. 6, virtually all resultant non-linearitiesof meter flow can be linearized so that the resultant output at photosensor 62 is linear with respect to changing flow.

In less exacting applications, a completely passive low friction linearmotion potentiometer may be substituted for the light-emitting diode 60,photocell 62 and power supply assembly. The potentiometer would bedriven directly from the diaphragm assembly resulting in a flow meterpossessing the advantages of being less complex and completely passive,but possessing the disadvantage of being less precise due to increasedfriction. The resistance versus displacement function of thepotentiometer may be tailored to compensate for various non-linearitiesmuch in the same manner as the neutral density wedge may now betailored.

The function of the electronic circuitry useful for both powering anddetecting the changing flow through the meter of this invention can beeasily understood with respect to FIG. 5. Assuming that remote dialingequipment B is placed intermediately of the meter mounted electroniccircuitry 70, and the telephone office mounted circuitry 90, sampling ofthe meter can occur. Specifically, remote dialing equipment B connectspower source 91 through a transformer primary 92 and secondary 93 acrosssampling conduits 71, 72. By supplying an alternating current sourceacross meter transformer primary 73, meter transformer secondary 74 isexcited to illuminate the light source 60. Similarly, and on the photosensor 62 side of the neutral density wedge 57, the alternating currentpath is bypassed at a capacitor shunt 75. The result is that the overallresistivity of the circuit can be measured across a correspondingcapacitor shunt 95 at readout 96 powered by a direct current powersource 97.

Thus, it is apparent that through connection across the single conduit71, 72, both powering and metering of the penetration of the neutraldensity wedge 57 between the light source 60 and the photo sensor 62 canoccur.

Typically, the alternating current voltage transmitted to the conduits71, 72 is in the range of 80 volts (RMS) dropping to 40 volts (RMS)dependent upon the length of the cable run. When the meter registershigh flow, a correspondent low impedance in the range of 100,000 ohms isregistered at photoconductor 62. When the meter registers low flow, ahigher impedance is registered which is tailored, either by the neutraldensity wedge, or other resistance used by the device.

It should be noted that the most likely malfunctions (a short circuit)produce an indication of high flow. Moreover, where insulation breaksdown between the two conduits 71, 72, an impedance far lower than the100,000 ohm level will result as a telltale of this type of malfunctionevent.

It should be understood that the invention herein disclosed will admitof modification. For example, the pressure transducers K and L shown inFIG. 1 can be modified as to their intermediate location betweenmanifolds and at the respective ends of cable runs. Moreover, while theparticular variable area orifice herein illustrated is preferred, otherorifice arrangements can be utilized. Likewise, the shape andconfiguration of the meter parts all preferably herein illustrated, canbe changed.

We claim:
 1. Apparatus for remotely monitoring air flow at a centralstation to the interior of a remotely located cable sheath surrounding aplurality of communication conduits, said apparatus comprising: a sourceof dehumidified air; an air conduit between said source of dehumidifiedair and the interior of said cable sheath for supplying dehumidified airto the interior of said sheath, a flow meter inserted in said airconduit proximate said sheath for passing at least part of the air therethrough to said sheath, said flow meter including a housing having aninlet for receiving at least part of said air, an outlet for dischargingat least part of said air, and a biased diaphragm mounted for movementwith respect to said housing responsive to changes in flow of saiddehumidified air from said conduit to said cable sheath, means fordefining an aperture in said diaphragm, a tapered member mounted to saidhousing and coacting with said aperture for defining changing air flowareas between said inlet and outlet upon changing concentric movement ofsaid aperture over said tapered member responsive to changes in fluidflow between said inlet and outlet; a member having variable opticaldensity within said meter operatively attached to said diaphragm forrelative movement to said meter with said diaphragm responsive to fluidflow; a light source in said flow meter on one side of said member ofvariable optical density; a photo sensor on the other side of saidmember of variable optical density for receiving from said light sourcea signal proportional to the diaphragm actuated movement of said memberof variable optical density; at least a pair of electrical conduitsextending between said central station and said flow meter; means forremotely monitoring and powering said light source and photo sensorthrough said pair of electrical conduits; means for connecting saidphoto sensor across said pair of electrical conduits to impart betweensaid conduits said signal proportional to the diaphragm actuatedmovement of said member of variable optical density; and meter means atsaid central power station connected across said electrical conduits forreading said proportional signal.